Genetics DNA, Genes & Chromosomes and mutations

M R S G R E N C EPRODUCTIONEPRODUCTION

What do these words mean? 1Gene 2DNA 3Chromosome 4Gamete

Nova – journey into DNA – (double click)

The human body is made up of around 60 trillion cells The nucleus of each cell contains your genetic material in the form of chromosomes Chromosomes are long lengths of DNA that has been coiled up

DNA can’t usually be seen in cell nuclei, but sometimes it coils up into short fat chromosomes that can be seen with a microscope. chromosomes Uncoiled DNA

Chromosomes can be seen in some of these plant cells, stained pink.

If the cells are broken, the chromosomes spill out, and can seen as rods.

Using an electron microscope, chromosomes can be seen more clearly.

A single chromosome is made of a very long molecule of DNA tightly coiled up into a short fat bundle. A gene is a short part of this DNA. There are about 2,000 genes spread along the length of each chromosome. Loops of DNA

A gene is a short length of the coiled DNA within a chromosome. Each gene controls one characteristic.

There are 46 chromosomes in each human cell. Each chromosome contains around 2,000 genes.

The 46 chromosomes can be arranged in order of size to form a karyotype. The chromosomes form matched pairs (except for the sex chromosomes). So you have two copies of each chromosome and two copies of each gene.

In summary… Chromosomes are long lengths of coiled up DNA found in the nucleus of every cell* Chromosomes contain genes (more on these later), which give the instructions for making the different proteins needed by each cell. There are 23** different ‘types’ of chromosome – each type always carries the same kinds of genes (e.g. the gene for making insulin is always on chromosome 11) Each nucleus in your body contains 2 copies of each type of chromosome**, so a full set contains 46. You inherited one copy of each type of chromosome from each of your parents. *apart from red blood cells **depending on whether you are male or female, the ‘sex’ chromosomes (called X & Y) can be an exception to this rule – which we’ll explain later

DNA – Deoxyribonucleic Acid Each chromosome is made up of a long-chain molecule called DNA. The DNA is tightly wound up to fit it into each chromosome In total there is around a metre of DNA inside each nucleus though it is very thin.

DNA – Deoxyribonucleic Acid What 3 main properties does DNA need to have? 1.To store genetic information 2.To replicate accurately when a cell divides 3.To control characteristics by making proteins

DNA – Deoxyribonucleic Acid The bases are always paired: A with T and C with G. This is complementary base pairing. DNA is a long chain molecule which has 2 strands coiled together in the shape of a double helix. The 2 strands are held together by bonds between chemicals called bases. There are 4 different bases – adenine (A), thymine (T), cytosine (C) and guanine (G)

DNA – Deoxyribonucleic Acid The 4 chemical bases are important for 2 reasons – can you think what these are? 1. Because of complementary base pairing, each DNA molecule can be easily copied. 2. Each DNA molecule is very long (millions of bases in one molecule). The order of the bases can be used to store large amounts of information.

DNA & Genes A gene is a ‘short’ length of DNA a few hundred bases long that codes for a particular protein or characteristic Sequence of amino acids in a protein

Genes All characteristics are controlled by genes, which are made of the chemical DNA. Organisms resemble their parents because they inherit genes through their parents’ sex cells (gametes) Create a Key Word Glossary: DNA Gene Chromosome Gamete

Genes All characteristics are controlled by genes, which are made of the chemical DNA. Organisms resemble their parents because they inherit genes through their parents’ sex cells (gametes) DNAA very long molecule found in the nucleus. Genes are made of DNA. Gene Part of a DNA molecule that controls a particular characteristic. Humans have about 25,000 different genes – the human genome. Chromosome A highly coiled-up DNA molecule, which can be seen with a microscope. In humans the DNA molecule is split into 46 sections, giving 46 chromosomes. The chromosomes form pairs, so there are really 23 pairs of chromosomes. Gamete A sex cell (i.e. egg or sperm cell). Gamete cells have half the normal number of chromosomes (23 in humans), so that the full number is restored on fertilisation.

Genes and Alleles A C T G G C G T T A A G C T A T C G A A T G C T A G G T C C T A G G C T T This is the base sequence of a gene for eye colour The protein that it codes for makes the iris brown A C T G G C G T T A T G C T A T C G A A T G C T A G T T C C T A G G C T T This gene also codes for the eye colour protein, but notice the subtle differences. The protein still does the same job but this time it makes the iris blue. Different versions of the same gene are called alleles

Mutation A mutation is a rare, random change in an organism’s DNA that can be inherited* *some mutations are somatic and only affect the individual in which they occur – they are not inherited or passed onto offspring A C T G G C G T T A A G C T A T C G A A T G C T A G G T C C T A G G C T T A C T G G C G T T A A G C A A T C G A A T G C T A G G T C C T A G G C T T Mutations occur when DNA is being copied prior to cell division This small change in the base sequence is the mutation

Mutation A mutation is a rare, random change in an organism’s DNA that can be inherited* A C T G G C G T T A A G C T A T C G A A T G C T A G G T C C T A G G C T T A C T G G C G T T A A G C A A T C G A A T G C T A G G T C C T A G G C T T The base sequence of a gene determines the shape and function of a particular protein. Many mutations are harmful because they result in non-functional proteins. This could lead to cancer or genetic diseases Some mutations are neutral as despite the change in the gene the same protein is still made Very rarely, mutations may be beneficial as they lead to ‘better’ proteins. These might provide a survival advantage and are the basis of natural selection.

Mutation A mutation is a rare, random change in an organism’s DNA that can be inherited* A C T G G C G T T A A G C T A T C G A A T G C T A G G T C C T A G G C T T A C T G G C G T T A A G C A A T C G A A T G C T A G G T C C T A G G C T T The base sequence of a gene determines the shape and function of a particular protein. Many mutations are harmful because they result in non-functional proteins. This could lead to cancer or genetic diseases Some mutations are neutral as despite the change in the gene the same protein is still made Very rarely, mutations may be beneficial as they lead to ‘better’ proteins. These might provide a survival advantage and are the basis of natural selection.

What causes mutations? A mutation is a rare, random change in an organism’s DNA that can be inherited Mutations are spontaneous and random events that occur during the copying of DNA. However, the probability of mutation is increased by exposure to: Ionising radiation e.g. gamma rays, X-rays & ultraviolet rays Chemical mutagens e.g. many of the chemicals in tobacco smoke. A chemical that brings about ‘cancer-causing’ mutations is called a carcinogen. In both cases, the mutations come about because they interfere with the process of DNA replication (copying).

Put these in order of size, from biggest to smallest 1Gene 2DNA 3Chromosome 4Gamete 5Nucleus 6Cell

1Cell 2Gamete 3Nucleus 4DNA 5Chromosome 6 Gene

Zoom into DNA from Cain

DNA – Deoxyribonucleic Acid